Throat Eroded??

[sethmstanton]

My dad has a .264 Win Mag w/ pre-64 Action. Hes had this gun for bout 30 years, but only really ever shot during deer season. We've been messing with all kinds of different methods for figuring out the distance to his landss.We've smoked bullets, and I just purchased the Hornady OAL Gauge. The thing works great on my .308 and the .243. Never more than a .001 difference.But on the .264 we cant get the same # twice. We've got numbers from 3.420 to 3.560. I know these guns were known for burnin out a barrel within 500 rds due to the high velocities and hot loads. So they began using stainless barrels and the problem was solved. I believe he has the stock chrome moly barrel on it now. My question is, are the large difference in numbers due to a worn out barrel? We've benn messin with this this for a couple weeks now tryin to get a good hard number and it just aint happining. Thanks guys.

Seth

 

[sethmstanton]

Re: Throat Eroded??

Bump

 

[Grumulkin]

Re: Throat Eroded??

The way to find out if the throat was eroded would be to look at it with a bore scope or make a chamber cast. I believe you can get the stuff to make a chamber cast from Brownel's.

I know the 264 Win. Mag. cartridge did erode throats rapidly but I think they went more than 500 rounds. What matters anyway is the accuracy obtainable from the barrel. If the accuracy is satisfactory, it doesn't matter how far the bullet is off the lands, etc. What kind of groups are you getting with the rifle?

 

[Greg Langelius *]

Re: Throat Eroded??

The .264WM is a special case where throats are involved. They were originally short throated as part of a strategy to achieve acceptable accuracy with acceptable chamber pressures. The Winchester Engineers designed the factory loading with a special "two-diameter" bullet, which started up front with a narrower 'bore rider' diameter that did not engrave, and a wider rear portion which did.

While this process works, it also creates a problem when attempting to handload using conventional bullets. In order to engage the rifling correctly, they need to be seated much deeper into the case than is the custom, which defeats much of the purpose of the magnum case capacity. The Sierra manual suggests that simplest and most effective solution is to have the barrel rethroated to more conventional specs by a professional gunsmith.

...Or; stick to Winchester commercial .264 WinMag ammo.

Greg

 

[sandwarrior]

Re: Throat Eroded??

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">The .264WM is a special case where throats are involved. They were originally short throated as part of a strategy to achieve acceptable accuracy with acceptable chamber pressures. The Winchester Engineers designed the factory loading with a special "two-diameter" bullet, which started up front with a narrower 'bore rider' diameter that did not engrave, and a wider rear portion which did.

While this process works, it also creates a problem when attempting to handload using conventional bullets. In order to engage the rifling correctly, they need to be seated much deeper into the case than is the custom, which defeats much of the purpose of the magnum case capacity. The Sierra manual suggests that simplest and most effective solution is to have the barrel rethroated to more conventional specs by a professional gunsmith.

...Or; stick to Winchester commercial .264 WinMag ammo.

Greg</div></div>

Wow! I learn something new every time I come here. The only 'double-diameter' bullet I knew of was the 7.5 Swiss. I wonder if this was some kind of method to overcome the headspacing on a belted cartridge accuracy issue?


Hogslife,

As you may already know the .264 case is a belted case which headspaces off that and not the shoulder like other cases. Make sure your .264 measuring case is seated all the way up belt to belt face. It should then just be a case of gently pushing the bullet to the lands. In the case of the .264 where erosion happens rather quickly you may have a lot of contact before you feel the friction. Just go very gently and feel for ANY change in resistance.

Lands will mostly erode from the top leading edge and sides of the leading edge first. The bottom front of the lands won't erode as quickly. Get a bright LED light and set the rifle up in a rest that you can look into the bore end of the chamber. What you need to look for is how sharp the leading edges of the lands look. After thirty years and a box or so of shells each year you may or may not still be able to see the front leading edge, but erosion shouldn't really be too bad. Erosion is sped up when the rifle is continually shot when the barrel heats up. Competition rifles tend to suffer a lot more erosion than do regular rifles with the same number of rounds through them for that reason.

Anyways, take a look and see what you can. You can see appreciable erosion without having to boroscope it.

 

[sethmstanton]

Re: Throat Eroded??

Great info guys. Definately check it out with the LED, and if that doesnt work I guerss we'll borescope it. Thanks again tfor the help.

Seth

 

[Hummer]

Re: Throat Eroded??

6.5MM Sierra bullets don't seem to mind jump so much and as some say as long as it is shooting don't worry about it but bear in mind there are some things you can do to increase barrel life.

As others have said don't shoot it continiously but I have found based on experimentation with two new rifles that I can slow throat erosion down by about 75%.
First off I have a Olympus Series 5 borescope I fell into and it shows all kinds of interesting things. I keep round log books with each rifle so I knew the history and I quickly determined that the reamer marks in the throats are gone at 150 to 200 rounds.

I initiated a new cleaning schedule on two new rifles. 308 and 30.06 which basically was I cleaned them just as soon as the last round was fired by running a sloppy wet bronze brush down them at least ten passes before the carbon residue had a chance to harden up on cool down. This is followed by two sloppy wet patches and rifle is cased "wet bore". With this enhanced cleaing schedule I was able to see reamer marks well beyond 800 rounds where before they were gone in 200.

For bore cleaner I use Ed's Red I made myself however I don't use the acetone.

Determining how much scrubbing is needed to remove the carbon depends on the surface finish of the barrel. I have one barrel that five passes and two wet patches will remove the carbon, others take ten, others 15 and I have one that one hundred cycles won't get all the carbon out.

Starting a frequent schedule with new tube will pay off for you down the road by being easier to clean and running longer. I saw a slave fixture for ammo testing once. There was no rifling for three inches in front of chamber. Rig still shot 1/2 MOA at 300 yards. It was cut off and set back and rechambered and still shot 1/2 MOA. It had this kind of cleaning schedule and scrubbed and cleaned immediately after firing.

I had another barrel I put on new and fired it one and clean with copper removing cleaner and it was still not broke in after 150 rounds. A looksee with bore scope revealed it was apparently rifled with a mill bastard file and a brick ! ! ! Top of lands were very rough.

I now brush after every yard line in high power matches.

 

[Greg Langelius *]

Re: Throat Eroded??

When casing a wet bore; it may pay to orient the rifle in the case with the scope down, to reduce the likelihood of goop drainage into the trigger mechanism. This is the opposite of how I suggest under other circumstances.

Normally, I suggest a rifle be cased with the scope oriented toward the case handle. This way, if the case gets dropped, the scope is less likely to smackdown against the casewall, possibly disturbing the basic optical alignment/zero.

Often, otherwise untraceable zero shifts will end up being traceable to this.

Greg

 

[sandwarrior]

Re: Throat Eroded??

Greg??

You sound like what I do sometimes...reading and thinking about one post, then nod off. When I wake up I post to something else.

We were talking about throat erosion. Case capacity...causes thereof?? Have some coffee in the am and talk to you then.

 

[Greg Langelius *]

Re: Throat Eroded??

Just responding to the post immediately prior, concerning putting a rifle into a case with a solvent soaked bore. I used to do that until I noticed the gooey mess of semi-congealed varnish that had taken up residence inside my trigger group.

Now I case soaking bores with the trigger upward to ward off this accursed plague...(the waving of severed checken feet should be saved for this particular stage...).

Also, seems I read somewhere (probably in a land far, far away, a long, long time ago, called The 'Hide), that hot bores and bore solvents are not an ideal mix. Kinda vague on the 'why' of it, but I let 'em cool first, myself.

Meanwhile, back at the ranch (the Lone Ranger, cleverly concealed as a pool table...; ah, yes, but that's another story for yet another day...), I was early schooled to not do as the above, because putting the trigger upward, (curiously...) also places the scope downward, and a roughly handled or dropped case can do bad things to optics and their mounts.

A quandry...; yes?

Greg

 

[sandwarrior]

Re: Throat Eroded??

Greg,

The point of your post as it applies to this thread then would be not damaging bores with solvent cleaning them hot? The only why of it would be a really hot bore might cause a chemical change in the solvent or allow the solvent to seep into the deepest minute cracks in the bore and possibly not come out for a while. The barrel would have to be extremely hot to go through 'cold shock' from the solvent and crack.

As the rest of the cleaning is concerned, yes I wouldn't leave a bore soaked with solvent to drain down into the trigger ass'y. I wouldn't leave where it would drain into the action either. I make it a point to leave the barrel pointed down. If the bore is left wet, it is only with one wet patch followed by an undersized dry patch. That leaves enough solvent in the barrel to work or at least loosen up the carbon and copper fouling for a better clean at home.

 

[Greg Langelius *]

Re: Throat Eroded??

I wasn't thinking thermal shock, and I'm still not thinking it. Otherwise...

 

[sinister]

Re: Throat Eroded??

Check chamber throat condition with a borescope. The RCBS/Stoney point should also be very useful.

Check your bullets with a comparator and micrometer to ensure you have uniform ogives, otherwise you're going to get 100 different length readings in a 100-round box.